OSTEOLOGY OF AMERICAN PERMIAN VERTEBRATES 417 



Until very recently our knowledge of the stegocephalian man- 

 dibular structure has been imperfect and more or less erroneous. 

 Branson for the first time recognized in an amphibian the presence 

 of a distinct prearticular, and correctly homologized what is now 



Fig. 18. — Trimerorhachis insignis; A, right mandible, from below; B, the same, 

 from above. Explanations as in Figs. 13 and 17. 



known as the true splenial with the infradentary of fishes. He 

 erred in uniting the postsplenial with the angular, and in calHng 

 the intercoronoid and precoronoid the splenial. He also identified 

 the true coronoid correctly. Watson very recently correctly 

 homologized the true splenial with the infradentary of Branson, 



